Polyaxial screws are known that include a threaded bone anchoring portion connected to an anchoring portion with a mechanical thread that is completely free in rotation around said threaded bone anchoring portion.
This freedom of movement of the mechanical thread anchoring portion with respect to the threaded bone anchoring portion is a source of some drawbacks when said screw is anchored in the vertebral body of a vertebra.
In fact, the mechanical thread anchoring portion is free from any pivoting around the threaded bone anchoring portion during the placement of the linking connector and the link rod by the surgeon.
This freedom of movement of the mechanical thread anchoring portion does not make it possible to position and keep the latter in a predetermined axial plane so the surgeon can mount the linking connector and the link rod.
The latter is required to keep the mechanical thread anchoring portion in a predetermined angular position with respect to the threaded bone anchoring portion fixed in the body of a vertebra during the placement of the linking connector and the link rod, making the mounting of the spinal device much more complicated.